Kicker reported that assistant coach Arno Michels was also joining the club from Mainz.

Mainz reacted with humor to the news, tweeting that it was now Dortmund's "coach-forge" along with a picture of current coach Martin Schmidt and under-23 coach Sandro Schwarz in Dortmund colors, suggesting they will be Dortmund coaches in 2020 and 2025, respectively.

Tuchel hasn't worked since resigning as Mainz coach after the 2013-14 season. He led the side to 65 wins and 44 draws in 170 league games after taking over from Klopp in 2009. He had been in talks with Hamburger SV recently about taking over the relegation-threatened side from next season. Hamburg re-appointed Bruno Labbadia on Wednesday.

Tuchel is seen as a natural successor to Klopp. Both favor a high-pressure game with the emphasis on quick attacks.

​Klopp's decision to quit after a difficult season surprised many. The 47-year-old German took over at Dortmund in 2008, leading the club to the Bundesliga title in 2011, the league and German Cup double the following year, and the Champions League final in 2013.

Dortmund was runner-up to Bayern Munich in the Bundesliga in 2013 and 2014 but its form slumped this season. The club made its worst ever league start and was in last place in February.

Dortmund only has the German Cup and European qualification to aim for this season. Saturday's 3-0 Bundesliga win over Paderborn moved the club to eighth, provisionally five points behind Schalke in the last Europa League qualification spot.

Dortmund fans celebrated the popular Klopp by chanting his name during the game, though he kept his emotions in check.

"Nobody wants to see that, when a 47-year-old man is sobbing uncontrollably on TV every week," Klopp said. "It will get really emotional again. But until then I have to wear a protective shield and not let it get to me as a person."